In response to the serious problems of adolescent sexually transmitted diseases and sexual risk-taking behaviors, this research will focus on the relationships between STD-related knowledge, attitudes, beliefs, and experiences, and adolescents' sexual behavior. An STD-specific form of the Health Belief Model will be used to test these interrelationships in a prospective study of 1,000 sexually active or inexperienced men and women, 21 years of age or less, over a one-year period. At Time 1, participants from four high school clinics and one community clinic will complete self-administered questionnaires to assess health beliefs about STDs, knowledge and beliefs about AIDS, future time perspective, health locus of control, and sexual behavior. Sexually active participants will also be offered screening for a wide variety of STDs. Compliance with STD screening, presence of infection, and sexual behaviors will be analyzed cross-sectionally in relation to health beliefs, knowledge and social-cognitive characteristics. One year later, at Time 2, subjects will be recalled for readministration of surveys and STD screening. Changes in health beliefs, knowledge, behavior and STD-status will be assessed as a function of age and of previous experience with STDs. Time 1 measures of health beliefs, attitudes, knowledge, and social-cognitive characteristics will be used to predict outcomes in STD status, sexual activity, and sexual risk behavior at Time 2.